It is generally known that there can be particles in a gas in which a plasma condition is generated by means of an electric discharge. The particles are, for example, specifically introduced into the plasma from the outside or are generated in the said plasma by means of a pre-determined process sequence (refer to, e.g. “Dusty Plasmas: Physics, Chemistry and Technological Impact in Plasma Processing” (ed. A. Bouchoule), J. Wiley & Sons, 1999). In this case, particularly an examination or manipulation of the particles in the plasma can be desirable. During the examination of the particles, for example, an interaction of particles (e.g. during the generation of so-called plasma crystals) or the development or the growth of the particles are to be characterised. The manipulation of particles can comprise, for example, a particle processing in the plasma (surface removal or surface separation) or the deposition of the particles on substrates, as is the case during the controlled deposition of polymorphic layers (Cabarrocas et al. J. of Non-Crystalline Solids 227-230 (1998) 871-875). In the deposition of polymorphic layers, the separation or the deposition of particles in a certain particle size distribution can be of interest. However, a practical method for the setting of a particle size distribution has not been available up to the present time.
Alternatively, the particles in the plasma or on a substrate can represent an undesirable contamination. As an example, during the manufacture of solar cells, wafers or components for the flat screen technology by plasma deposition, the quality and the failure rate of the products can be substantially determined by the capability to keep away the disturbing particles from the substrates to be coated. Particles can cause local discharges on the substrate and, subsequently, holes in the layer through which the image quality, for example, of a flat screen is diminished.
One cause of the substrate contamination is that, after a coating operation when the plasma is switched off in a plasma reactor, the particles formed in the plasma with typical dimensions in the nm range to the um range carry an electric net charge (typically a negative charge), whereas the substrate surface has an opposing charge. This leads to a previously unavoidable particle movement to the substrate surface, even if the plasma coating is performed on vertically aligned substrates (Ivlev et al. “Decharging of Complex Plasmas: First Kinetic Observations” in “Phys. Rev. Lett.”, Volume 90, Page 5). The problems mentioned here occur particularly with the plasma deposition on large substrates with typical diameters in the dm range to the m range.
With the applications for the examination or manipulation of particles in the plasma as well as with the particle contamination, there is generally an interest in exerting influence on the location, distribution and/or movement of the particles in a pre-determined manner. It is proposed in WO 99/52125, in a plasma reactor with additional electrodes or with the use of a so-called adaptive electrode with a plurality of partial electrodes, to set or to change the electric field statically or with low frequency in such a way that the particles assume a certain spatial distribution over the substrate in the plasma reactor. However, this technique can be disadvantageous in that the defined objectives of examining or manipulating particles in the plasma can only be solved to a limited extent and that the deposition on the substrate reproduces the structure of the electrodes.